Many golf balls are commercially available, but they are typically classified into two piece solid golf ball and thread wound golf balls. The two piece solid golf ball consists of a solid core of molded rubber material and a cover of a thermoplastic resin (e.g. ionomer resin) on the solid core. The thread wound golf ball consists of a solid or liquid center, a thread wound layer formed on the center and a cover of an ionomer resin balata or the like on the thread wound layer.
The two piece solid golf ball, when compared with the thread wound golf ball, has better durability, flight performance and longer flight distance because of a larger initial velocity upon hitting. The two piece solid golf ball is generally approved or employed by many golfers, especially amateur golfers. On the other hand, the two piece solid golf ball has poor shot feel at the time of hitting and poor controllability at approach shot because of a low spin rate. The thread wound golf ball has better shot feel and better controllability during an approach shot than the two piece solid golf ball, but also has less flight distance and less durability.
An attempt was made to improve the shot feel of the two piece solid golf ball, by preparing a soft type two piece solid golf ball having a softer core. However the soft core adversely affects on impact resilience, thus resulting in the reduction of flight distance and the deterioration of durability.
Then, it was proposed that an intermediate layer be placed between the core and the cover of the two piece solid golf ball to keep the balance between flight performance and shot feel at the time of hitting. For example, Japanese Kokai Publication Hei 4 (1992)-244174 taught a mixture of a block copolymer of polyamide and an ionomer resin as the intermediate layer. This golf ball, however, showed relatively poor impact resilience and poor flight distance. Japanese Kokai Publication Hei 6 (1994)-218078 taught that the intermediate layer is made from an ionomer resin and the cover is formed from a soft elastomer, such as rubber or balata. However, the use of ionomer resin in the intermediate layer adversely effects the shot feel at the time of hitting. In Japanese Kokai Publication Hei 6 (1994)-142228, a use of a mixture of a polyether-ester thermoplastic elastomer and an ethylene-(meth)acrylic acid copolymer ionomer is suggested. This does not result in shot feel and impact resilience.
Japanese Kokai Publication Hei 7 (1995)-171863 suggest that a mixture of a polyamide and an ionomer resin is used as the intermediate layer. However, the resulting golf ball has the benefit of high hardness, but poor impact resilience and therefore is not sufficient for keeping the balance between flight distance and shot feel at the time of hitting.